Gravity measuring instrument



N0v- 18, 1941. J. A. MARciHAND GRAVITY MEASURING INSTRUMENT Filed sept. 2, 1958 y 2 Sheets-Sheet 1' IAEA".

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' 2. Sheets-Sheet 2 Nav. 1s, `1941.`

J. A. MARCHAND GRAVITY MEASURING INSTRUMENT Filed Sept.l 2, 1938 atented Nov. 18, 1941 s PATENT OFFICE 2,263,096 I GRAVITY MEAsUmNG INSTRUMENT Joseph A. Marchand, Houston, Tex., assigner of fifty-live per cent to Bailey Balken, Houston,

Tex.

Application September 2, 1938, Serial No. 228,173

' (Cl. zes- 1.4)

5 Claims.

This invention relates to a gravity measuring strument, and it has special reference to` an .strument of this character, the purpose of hich is to measure the force of gravity at variis terrestrial ,points in order to take readings lom which may be determined, with reasonable irtainty, the subsurface formations occurring at ich terrestrial points.

Surveys of this character have been found to e of great value in locating petroleum bearing nd other subsurface formations, and the instrullent of the invention is well adapted to this urpose.

One object. of the invention is to provide r`a ravity measuring instrument of relatively simle, compact and rugged construction, and of mall size, whereby it may be moved from point a point readily and without danger of injury o its sensitive parts.

Another object. is to provide for ready adjustnent of the sensitive parts of the instrument to .ccommodate them to the taking of readings at oints where marked variations in the force of gravity occur.

A further object is to provide a construction vherein the scale of the instrument, and `parts lssociated therewith, are protected against ac- :umulation of dust and foreign matter and their iccuracy in taking readings thereby enhanced.

Another object is'to provide means for proiucing areadable image of the scale of the instrument thereby making possible the reading of ahe scale free from possibilityof inaccuracy or obscurity which might be incident to direct readlng of the scale.

A still further objectof the invention is to provide means whereby the sensitivity of the instrument may be so adjusted that. the movement of its moving parts will be appropriately accommodated to the scale fromfwhich 'readings are taken, change of this adjustment for marked differences in the force of gravity at various terrestrial points being provided for. as hereinbefore indicated.

An additional object is to provide for attachment ofthe counterbalanclng resilient means or spring of` the instrument in such a manner as to guard against error directly referable to temperature changes. j

With the foregoing and other objects and advantages in view, the invention contemplates a ably being in the form of a tensioned resilient i member, a pendulum carried by said beam and oscillatable therewith in response to the influence of gravity upon said mass or weight, the

` pendulum preferably being a weighted tube, scale gravity measuring-instrument of what may be termed a pendulum-actuated balance type, including a pivoted beam carrying a mass or weight `and counterbalanclng means therefor, both said means having associated light projecting means for casting its image in position to be read with respect lto the position of the pendulum, means for use in reading said scale means, and means for adjusting said weight and' counterbalance means to effect desired oscillation characteristics in Isaid pendulum, al1 as will be explained hereinafter more fully and nally claimed.

In the accompanying drawings illustrating lthe invention, in the several figures of which like parts are similarly designated:

Fig. 1 is an axial sectional elevation of an instrument embodying the features of the invention, taken on the lines l--l of Figs. 2 and 4;

Fig. 2 is an-axial sectional elevation of parts of the instrument, taken atjright angles to the section of Fig. 1 and upon the line 2--2 of Fig. 3;

Fig. 3 is a transverse sectional elevation taken on the line 3 3 of Fig. 1;

Fig. 4 is a transverse sectional elevation on the line 4--4 of Fig. 1;

Fig. 5 is a perspective view of the beam pivot; and

Fig. 6 is a schematic view illustrating the variations in the effective lever arms of the beam as determined by adjustment of the weight and counterbalance means thereof, respectively.

The operative parts of the instrument are carried by a relatively heavy mounting member l of substantially cylindrical form and of -suftlcient bulk and such material as normally to prevent excessive rapid temperature vchanges in the instrument. This member is suitably formed to receive and support a beam 2 mounted on appropriate pivotal supports 3 which are preferably taken of the'crossed ribbon type shown, the ribbons 4 of each support being crossed and having their respective ends secured in` slots in the rsupport brackets 5 and 6. These ribbons are preferably at substantially right angles to eachother and make equal angles with the brackets 5 and 6.

They are also preferablyarranged so that their point of intersection will be substantially midway f between the brackets 5 and 6.

Normal lto the axis of the pivotal supports'3 and rigidly depending from the beam 2 is a pendulum' member 1 preferably in the form of a tubular truncated cone and carrying at. its

lower end a stabilizing weight 3. This pendulum swings in response to the force of gravity acting upon a weight 3 adjustable longitudinally of a post Il and xed in adjusted position thereon by a set screw II, the post. I being carried adjacent to one end of the beam 2.

Resilient counterbalance means, preferably in the form of a tension spring I2, are connected between a point adjacent to the opposite end of the beam 2 and a xed part of the mounting member I. Adjustment of the point of connection of the spring I2-with the beam 2 is allorded by a block I3 axially slidable in a tube Il carried by the beam 2, iixing of desired adjustment being accomplished by a cap screw I5 carried by the block I3 and extending through a slot I6 in the tube Il against the walls of which it may be tightened. Provision for adjusting the tension of the spring is afforded by a threaded stem I1 axially slidable in a fixed bracket I3 and forming an abutment for an adjusting nut I9 engaging the thread of the stem I'I.

Itwill be noted that both ends of the spring I2 are connected with their respective adjusting means by iilamentary members 23 of suillcient tensile strength to answer their Dlll'POSe as connectors, but of such little body as to be incapable of appreciable transfer of heat between the spring and the parts to which it ls connected, and to provide a highly exible coupling without appreciable elastic hysteresis or mechanical stress.

Fixed within the member I in axial alignment with the normal vertical axis. of the tubular pendulum 'I is the scale apparatus, including a housing 2| in whichare assembled in predetermined optical arrangement a lamp 22, condensing lens 23, translucent scale plate 24 and image lens 25, with which latter cooperates a viewing lens 26 carried by the pendulum 1 and optically associated with the lenses 21 and 23 of the relatively fxed eye piece 29, the lens 21 preferably bearing a hair line, as may also the lens 26, so that the extent of movement of the pendulum with relation to the image of the scale plate projected between the lenses 25 and 26 may easily be read.

It will be noted that the scale plate 24 is enclosed dust-tight within the housing 2l, and hence its workings will not be blurred or confused by particles of dust or foreign matter which might otherwise settle upon it. If any I dust or other foreign matter should settle upon the lenses 25 and 26 it will be apparent that the projected' image of the scale will not be obscured thereby as any such foreign matter will be out of focus with respect to the scale plate and 'will not appear in the image thereof.

To determine the sensitivity of the instrument, the pendulum 'I must ilrst be adjusted to its slowest constant speed ofosclllation bythe raising or lowering ot the mass or weightv 3 and of the point'of attachment of spring I2 by raising or lowering the block I3, or both may be raised or lowered to satisfy the equilibrium period of the entire system.

The sensitivity referred to is the sensitivity oi the instrument to variations in the force of gravity exerted on the mass or weight l. Such variations may be very slight for the purpose of ascertaining the presence or absence of petrole- To explain further, if the pointof connection at I3 were directly at the outerend of the beam 2, and the mass or weight 9 directly at the other end of the beam, the adjustable supporting means I4 and Il), thereforev being omitted, then the period of oscillation of the pendulum about its pivots 3 would be much shorter and the instrument would therefore be less sensitive and much harder to read.

By adjusting the point of connection I3 and the mass or weight 9 to vary the lever arms from the axis of the pivots 3, the period of oscillation ismade much .longer and the instrument is therefore more sensitive and easier to read.

. prior and vsubsequent to the adjustment.

readings taken subsequent to adjustment are,

Fig. 6 illustrates diagrammatically the variations in the effective lever arms afforded by adjustments of the point of connection I3 and the mass or weight 9.

After the adjustments of these members upon their supports I4 and N to attain the desired sensitivity of the whole system of the instrument, the mounting member and associated parts are enclosed in a suitable case 30 and any further adjustments found necessary are made by actuation of the nut i9 to alter the position of the threaded stern I'I and the tension of the spring I2, thus to compensate for any changes, plus or minus, in the force of gravity acting upon the mass cr weight 3 which might be encountered in the field after leaving the laboratory.

For example, if the force of gravity or the mass or weight 3 increases or decreases, it is necessary, in order to bring the instrument into proper balance, to either decrease or increase the tension of the spring I2. 4

It will be obvious that such`adjustments are necessary due to the limited range of the scale and the consequent limited measurable swing of the pendulum. Hence for those changes in the force of gravity which would move the pendulum out of the readable scale range, adjustment must be made to appropriately limit the swing of the pendulum. Thus, when the nut I9 is adjusted, the operator observes the scale and notes the number of units on the scale through which the Apendulum is swinging. Thereby he is enabled to determine the effect of the adjustment and to know the relationship between readings taken The either added to or subtracted from the number of units of the adjustment depending upon the sense of the adjustment.

It will be apparent, therefore, that, in use, after proper adjustments are made, readings of the relative force of gravity for any particular location may be made by viewing through the eye piece 23 and the lens 26 of the tubular pendulum the range of movement of the pendulum with relation to the graduations of the image of the scale.

The crossed ribbon pivotal supports will proy vide for the support of the pendulum with a minium or the like in the subsurface formations by reason of the structure of such formations. In

lother words, the pull of lgravity varies with the' subsurface structure.

mum of friction, ancll without interference due to accumulation of dust and dirt, and will tend to compensate for what might otherwise result in changed reading due to temperature changes. Thus if the temperature rises and the ribbons expand tending to lower the pivotal axis as well as the pendulum, this will be compensated for by the simultaneous expansion of the material o! the brackets 5 and I between the ends of the respective ribbons, which latter expansion would tend to raise the pivotal axis and the pendulum.

Various changes and modifications are considered to be within the spirit of the invention and the scope of the following claims.l v

What I claim, is: i

1. In a gravity measuring instrument, a beam pivoted substantially midway of its length, a pendulum secured to and rigidly depending from said beam in vertical alignment with its pivot, a gravity responsive mass carried adjacent to one end.

and above said beam, counterbalance means .connected adjacent to the other end and above said beam, andmeans for individually adjusting the vertical position of said mass and the point of connection of said counterbalance means with reaacsgooe end and extending upwardly therefrom, a mass carried by said support member, counterbalance means including a tubular support member attached to the beam adjacent the other end there-4 of, an anchor member mounted in said'tubular member, a tension spring having one of its ends lconnected tosaid anchor member and its opposite end connected to said iixed part, means for individually adjusting the position of said mass 10 upon the nrst mentioned support member and said anchor member within the tubular member,

spring having its opposite ends attached to the i iixed part and the anchor member, and means for individually adjusting the position oi said mass and the anchor member with respect to the pivot of said beam to thereby vary the period of oscillation of said pendulum. v

3. In a gravity measuring instrument, a relatively iixed part, a beam pivoted substantially midway or its length to said nxed part, a pendulum secured to and rigidly depending from said beam in vertical alignment with itspivot, a support member attached to the beam adjacent one and means for varying the tension oi said spring by adjustment of its connection with the iixed part, to thereby vary the period of oscillation o! said, pendulum;v

4. In a gravity measuring instrument, a tubu-` lar pendulum member carrying a lens at its lower swinging end, scale means arranged adjacent to the lower swinging end of said pendulum member, a lens system ior projecting an image oi said scale means in position to be read in relation to the movement of said swinging end and means for viewing said image through said tubular pendulum member and. the lens carried at the end thereof. h

5. In a gravity measuring instrument, an eye piece and means for projecting a scale image in' axial alignment, a tubular pendulum member in axialv alignment when at rest with said eye piece and image projecting means and having its A swinging ,end movable with respect to said Vscale image, said eye piece furnishing a means of viewing said scale image through said pendulum member to read the extent oi! oscillation of said swinging end.

` JOSEPH A. MARCHAND. 

